It was always a little difficult telling exactly whose dog Pluto was. Originally,
he was developed because Walt thought it would be good for Mickey to have
a pet. However, he has been at times taken care of by Minnie and Donald
as well. He spent a small time in the Army, where he discovered Chip 'n'
Dale and brought them into national prominence.
But he also seems to have had a lot of time for having a life of his
own. Pluto had two great loves in his life, Fifi and Dinah. And any number
of kids who he could never deny parentage of, including the five puppies
in "Pluto's Quin-puplets" and one specifically named "Pluto, Junior."
There has also been a lot of argument about what kind of dog Pluto was,
especially when compared to the other famous Disney dog, Goofy. But Pluto
was always Mickey's dog, and in the words of Mickey, "He's just a mutt."
Curiously though (and unfairly, in this authors opinion) Pluto was the
only standard Disney character not included when the whole gang was reunited
for the 1984 featurette Mickey's Christmas Carol.
Although Pluto never spoke a word (save for one brief second in "The
Moose Hunt") his woofs and noises were provided at various times by Pinto
Colvig (also the voice of Goofy), Lee Miller, and Jimmy MacDonald (who also
took over the voice of Mickey Mouse after Walt Disney quit providing it.)